role of INterstitial Solutes and diffusive Processes In the plasticity of Refractory high entropy Alloys – INSPIRA

1. Atomistic simulations
As a starting point, we use molecular static or molecular dynamic simulations based on interatomic potentials available in the literature. Such simulations enables to understand the elementary mechanisms by incorporating the details of atomic interactions. However, the space and time scales accessible with such techniques remain limited, and cannot capture long-range elasticity and diffusive phenomena.

2. Elastic models
To overcome the limitations of atomic simulations, we also develop continuous elastic models that treat the dislocation as an elastic line interacting with obstacles. The calibration of the properties of the dislocation (stiffness, mobility) and the obstacles (random stress field, point obstacle strength, Peierls barrier, etc.) is however based on atomistic calculations. This type of continuous approach also enables to reach diffusion time scales, out of reach of molecular dynamics.

1. We have developed an elastic model to study the interactions between a dislocation and a stress field emerging from a random solid solution. In order to validate this approach, we applied it to the model case of concentrated Al-Mg alloys, highlighting the influence of the anisotropy of the stress field correlations on the mobility of the screw and edge dislocations.
2. The work carried out by Bassem Sboui during his first year of PhD focused on the transfer of the elastic description of random alloys to concentrated alloys of BCC structure which require a more complete formulation. This new description remains analytically tractable and provides (among other things) a prediction for the mean square displacement of atoms with respect to their atomic site. However, the model tends to underestimate this quantity for systems where the species present strong heterogeneities of elastic constants (such as the system of interest NbMoTaWV). We have developed a model system in order to highlight this elastic modulus effect often neglected in the hardening models proposed in the literature.

To be determined

I. Peer reviews articles:
A. Rida, E. Martinez, D. Rodney, P.A. Geslin. ‘’Influence of stress correlations on dislocation glide in random alloys.’’, Physical Review Materials 6, 033605, March 2022
DOI : doi.org/10.1103/PhysRevMaterials.6.033605
HAL : hal.archives-ouvertes.fr/hal-03616640

II. Conferences:
1. 12/2021. MRM – Japan (remote oral) : Pierre-Antoine Geslin, Ali Rida, David Rodney. Interplay between dislocations and correlated stress environment in random alloys
2. 02/2022. TMS – USA (remote oral) : Pierre-Antoine Geslin, Ali Rida, David Rodney. Concentrated random alloys : from stress correlations to dislocation depinning
3. 06/2022. ICMSA – France (on-site oral) : Bassem Sboui, David Rodney, Pierre-Antoine Geslin, Elastic model of BCC high entropy alloys.
4. 11/2021. Annual meeting GDR HEA, Paris (on-site oral) : Bassem Sboui, David Rodney, Pierre-Antoine Geslin. Study of the plasticity of refractory HEA alloys by atomistic and continuous
models.
5. 04/2022. Colloque Plasticité, Toulouse (on-site poster) : Bassem Sboui, David Rodney, Pierre-Antoine Geslin. Elastic model of BCC high entropy alloys

Refractory high entropy alloys are known to retain exceptional mechanical properties at high temperature, with possible applications of these materials in extreme condition environments. The development of quantitative models able to predict the mechanical properties of these alloys as function of their composition, temperature and strain-rate would allow to speed-up considerably their development. However, the models currently available do not account for the role of interstitial solutes and diffusive mechanisms operative at high temperature. In this project, I propose to overcome these limitations by developing a multi-scale approach taking into account these mechanisms. Atomistic simulations will allow to parameterize a continuous model of a dislocation interacting with interstitial solutes. Second, the coupling of this model with interstitial diffusion will allow to investigate their influence on the mechanical behavior of the alloy (dynamic strain aging).